Preselector interference rejection and dynamic range extension

ABSTRACT

A wireless telemetry module and associated method reject interference in a received signal. The wireless telemetry module includes an antenna receives a communication signal transmitted at a desired channel frequency and having a channel bandwidth. A transceiver is controlled to operate in receiving and transmitting modes by a processor. An interference rejection module receives control signals from the processor corresponding to the desired channel frequency and is coupled between the antenna and the transceiver when the transceiver is operating in the receiving mode.

TECHNICAL FIELD

This disclosure relates generally to telemetry modules for medicaldevice systems and, in particular, to a telemetry module includinginterference rejection.

BACKGROUND

Medical devices often include telemetry circuitry for wirelesslycommunicating with other devices or monitors. For example, animplantable medical device typically includes a telemetry module capableof bidirectional communication with an external programmer or homemonitor for programming and adjusting operating parameters in theimplanted device and for retrieving data from the implanted device.

In the past, implantable medical device telemetry systems required aprogramming head including an antenna to be held directly over theimplanted device. Advances made in telemetry systems allow wirelesscommunication over a distance of a few meters, sometimes referred to as“distance telemetry”, without the use of a programming head. Telemetrymodules incorporated in implantable devices are designed to operateusing a relatively low current to prevent excessive battery drain whichwould shorten the longevity of the implanted device. In the externalprogrammer, home monitor or other device communicating with theimplanted device, the telemetry module needs to be sensitive to thedesired signals but can be susceptible to interference both within thecommunication bandwidth and outside the communication bandwidth.Undesired interference signals can block or impair receiving operationsof a low dynamic range receiver. It is desirable to improve thetolerance of low dynamic range telemetry systems to interference signalsin medical device systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of one embodiment of a medical devicesystem enabled for wireless telemetry communication.

FIG. 1B is schematic diagram of an alternative embodiment of a medicaldevice wireless telemetry communication system including an interferencerejection module.

FIG. 2 is a functional block diagram of one embodiment of a telemetrymodule including an interference rejection module (IRM).

FIG. 3 is a flow chart of one embodiment of a method for rejectinginterference during wireless telemetry communication.

FIG. 4 is a plot of the insertion loss of an intermediate frequencyfilter appropriate for use in the IRM of FIG. 2.

FIGS. 5A through 5E are plots of the output signal of an IRM for fivedifferent communication channel frequencies.

FIG. 6 is a functional block diagram of another embodiment of atelemetry module including an IRM.

FIG. 7 is a flow chart of another method for rejecting interference in amedical device telemetry module.

DETAILED DESCRIPTION

In the following description, references are made to illustrativeembodiments. It is understood that other embodiments may be utilizedwithout departing from the scope of the invention. For purposes ofclarity, the same reference numbers are used in the drawings to identifysimilar elements. As used herein, the term “module” refers to anapplication specific integrated circuit (ASIC), an electronic circuit, aprocessor (shared, dedicated, or group) and memory that execute one ormore software or firmware programs, a combinational logic circuit, orother suitable components that provide the described functionality.

FIG. 1A is a schematic diagram of one embodiment of a medical devicesystem enabled for wireless telemetry communication. An implantablemedical device (IMD) 10 is shown implanted in a patient's body 8. IMD 10may correspond to numerous types of implantable devices includingpacemakers, cardioverter defibrillators, ECG recorders, hemodynamicmonitors, drug pumps, neurological stimulators, or any other implantabledevice implemented to monitor a physiological condition and/or deliverya therapy. IMD 10 typically includes a hermetically sealed housing 12,which encloses a power supply and electronic circuitry (not shown forthe sake of simplicity) for controlling device functions. IMD 10includes a wireless telemetry module 14 capable of bidirectionalcommunication with an external device 18 via link 16.

External device 18 may be implemented as a programmer used to program anoperating mode and associated operating parameters in IMD 10.Programming data is transmitted from external device 18 to IMD 10 vialink 16. External device 18 may additionally or alternatively be used tointerrogate IMD 10 to retrieve data acquired by IMD 10. Retrieved datamay include physiological data recorded by the IMD or collected in realtime as well as data relating to IMD 10 performance or functionalstatus, for example device-related data obtained during self-diagnosticfunctions performed by the IMD. Thus, external device 18 may beimplemented, for example, as a home monitor or a clinical programmer.External device may also include patient monitoring functions, such asECG recording, blood pressure monitoring, or the like. In variousembodiments, external device 18 may be capable of programming IMD 10,storing or processing data retrieved from IMD 10, transmitting orreceiving data to/from a centralized patient management database orother networked location, and sending or receiving alerts or othernotifications. The overall functionality of external device 18 may varybetween embodiments but will at least include wireless telemetriccommunication with IMD 10 via link 16 for transferring data to/from IMD10.

As such, external device 18 is provided with a telemetry module 20including an antenna 25 for receiving and transmitting signals to IMD10, a transceiver module 24, also referred to herein simply as“transceiver”, and a processor 22 or other control circuitry forcontrolling the function of telemetry module 20. Telemetry module 20further includes an interference rejection module (IRM) 30 which couplesantenna 25 to transceiver module 24 during receiving operations. IRM 30is coupled to transceiver module 24 via switches 26 and 28 controlled byprocessor 22 via control signal 32. During transmission operations,processor 22 provides a control signal 32 which causes switches 26 and28 to switch to a transmission pathway state. IRM 30 is bypassed duringtransmission operations. Transceiver 24 transmits a communication signalvia switch 28, transmission pathway 34, switch 26 and antenna 25. Thecommunication signal is received by IMD 10 via wireless communicationlink 16.

During receiving operations, processor 22 is configured to switchswitches 26 and 28 to a receiving pathway state (as represented inFIG. 1) using control signal 32. IRM 30 is coupled to antenna 25 viaswitch 26 and to transceiver 24 via switch 28. In this way, transceiver24 receives a wireless communication signal transmitted by IMD 10 vialink 16 and a receiving pathway 36 that includes IRM 30. The signaltransmitted by IMD 10 is received by transceiver 24 via antenna 25,switch 26, IRM 30, and switch 28. The communication signal undergoesinterference rejection by IRM 30 prior to being received by transceiver24. As will be described in detail herein, IRM 30 reduces thesusceptibility of transceiver 24 to interference thereby extending thedynamic range of telemetry module 20.

The IMD telemetry module 14 is not shown in detail in FIG. 1A, but it isto be understood that telemetry module 14 may include componentscorresponding to those described for telemetry module 20. Generally, areceiver implanted in the body will be less susceptible to interferencethan an external receiver because the patient's body acts to attenuateinterference signals. Thus, an IRM 30 included in an external device 18as shown in FIG. 1 may be optional in an associated implantable device10. It is recognized, however, that an IRM 30 may be included in anyexternal or implantable medical device intended to communicate with anyother external or implantable medical device. A telemetry moduleincluding IRM 30 is not limited to use in an external devicecommunicating with an implantable device. For example, embodiments of atelemetry module described herein may be implemented in a medical devicesystem including two or more external devices communicating wirelesslywith each other, two or more implantable medical devices implanted in apatient's body and communicating with each other, or any combination ofexternal and implantable devices. A medical device in which telemetrymodule 20 is implemented is referred to herein as a “host device.”

Furthermore, it is recognized that embodiments of an interferencerejection module described herein are not limited to use in medicaldevice telemetry systems but may be implemented in any device intendedto receive wireless telemetry signals. Wireless telemetry signals mayinclude signals in a radio frequency range, ultrasonic range or infraredrange. Illustrative embodiments described herein relate to RF telemetrycommunication, however, the interference rejection methods and apparatusdescribed herein are not limited to RF telemetry systems.

Components included in the implantable telemetry module 14 and theexternal telemetry module 20 such as antenna 25, transceiver 24 andprocessor 22 may generally correspond to those included in telemetrysystems described, for example, in U.S. Pat. No. 6,482,154 (Haubrich etal.), incorporated herein by reference in its entirety.

FIG. 1B is schematic diagram of an alternative embodiment of a medicaldevice wireless telemetry communication system including an interferencerejection module. Identically numbered elements correspond to thosedescribed above in conjunction with FIG. 1A. External device 118includes a telemetry module 120 enabled for simultaneous bidirectionalcommunication in a full duplex mode. The system shown in FIG. 1A cangenerally be referred to as a half-duplex system in that transmittingand receiving occurs non-simultaneously, for example in time divisionduplexing controlled by processor 22. In a full duplex systemtransmission and receiving can occur simultaneously using differentoperating channels. In telemetry module 120, transceiver 24 is coupledto antenna 25 via diplexers 128 and 126 which control the transmissionof data using a different channel frequency than the channel frequencyused for receiving, i.e., frequency division duplexing. IRM 30 iscoupled between diplexers 128 and 126 along the receiving pathway 36.

Embodiments described hereafter refer generally to a telemetry moduleoperating in time division duplexing and including pre- and post-IRMswitches operating as described above and shown in FIG. 1A. It isrecognized, however, that any of the embodiments described herein mayalternatively be implemented in a full duplex system incorporatingdiplexers as shown in FIG. 1B.

FIG. 2 is a functional block diagram of one embodiment of a telemetrymodule 200 including an IRM 201. Telemetry module 200 includes anantenna 202, IRM 201, pre-IRM switch 204, post-IRM switch 206, processor210 and transceiver 208. Antenna 202 is provided for receivingoff-the-air radio frequency (RF) signals transmitted by another medicaldevice 190 and for transmitting communication signals from transceiver208. Processor 210 controls transceiver 208 to operate in either atransmission mode or in a receiving mode. During a transmission mode,processor 210 provides a control signal 260 to pre- and post-IRMswitches 204 and 206 to select a transmission pathway from thetransceiver RF antenna port 250 to antenna 202 via switches 204 and 206bypassing IRM 201. During a receiving mode, processor 210 provides acontrol signal 260 to pre- and post-IRM switches 204 and 206 to select areceiving pathway from antenna 202 through IRM module 201 to transceiver208.

Various control methods may be used for controlling the timing ofalternation of transceiver 208 between a transmitting mode and areceiving mode. In one embodiment, processor 210 controls transceiver208 to operate in transmitting and receiving modes in alternating blocksof time, which may be further divided into frames, for transmitting orreceiving data. Processor 210 selects the transmission or receivingpathway accordingly by providing control signal 260 to cause pre- andpost-IRM switches 204 and 206 to switch between states, thus selectingthe transmission pathway bypassing IRM 201 or the receiving pathwayincluding IRM 201.

During a receiving mode, antenna 202 receives a signal 203 whichincludes a desired communication signal 195 transmitted by anotherdevice 190 and can include various interference signals. Signal 203received at antennal 202 can be referred to as a “composite signal” inthat antenna 202 will receive the desired communication signal 195 aswell as interference signals that may exist across a spectrum offrequencies. The desired communication signal 195 is a wirelesstelemetry signal transmitted from another medical device 190 at aselected channel frequency having a relatively narrow channel bandwidth.The received signal 203 may further include both in-band interferers,i.e. noise signals having frequencies falling within a range ofcommunication channel frequencies over which transceiver 208 isconfigured to operate, and out-of-band interferers, i.e. noise signalshaving frequencies outside the range of communication channelfrequencies. For example, if telemetry module 200 is configured tooperate over a range of 401 to 406 MHz, encompassing a range of MEDS andMICS channels commonly used in medical devices, in-band interferers arethose falling within the 401 to 406 MHz range and out-of-bandinterferers are those falling outside the 401 to 406 MHz range. As such,while “signal” 203 is referred to herein in the singular from, it isrecognized that “signal” 203 will typically include a spectrum of signalfrequencies including the desired communication signal frequency and thefrequencies of any in-band and out-of-band interferers.

These in-band and out-of-band interferers, also referred to generallyherein as “interference signals”, can impair the sensitivity oftransceiver 208, particularly when distance telemetry is performed suchas across a room, e.g., across about 3 meters or more. At shorterdistances, e.g., less than one meter, undesired interferers may betolerated by a low dynamic range receiver. However, at greaterdistances, a higher power transmission signal is typically required tocompensate for interferers. To avoid requiring higher power transmissionsignals while still allowing successful communication with a low dynamicrange receiver, IRM 201 is implemented in telemetry module 200 toattenuate interference signals while having a non-significant net effecton the received communication signal 195. Thus, IRM 201 as describedherein effectively adapts a low dynamic range telemetry module tofunction as a relatively higher dynamic range telemetry module withoutaltering the transceiver itself.

IRM 201 includes a pre-selector filter 220, low noise amplifier 222, anoptional attenuator 224, an image filter 226, a pre-mixer 228, anintermediate frequency (IF) filter 230, a post-mixer 232, gain control240, local oscillator 234, loop filter 236, and synthesizer 238.Pre-selector filter 220 is provided as a bandpass filter selected topass a range of frequencies corresponding to the range of operatingchannel frequencies to be received by transceiver 250. Pre-selectorfilter 220 will attenuate out-of-band interferers but does notsignificantly alter in-band interferers. In one embodiment, pre-selectorfilter 220 passes frequencies in the range of 401 to 406 MHz, associatedwith the MEDS and MICS RF channel range.

Low noise amplifier 222 reduces insertion loss of the communicationsignal 195 by amplifying the output of pre-selector filter 220. Imagefilter 226 suppresses undesired interferers before mixing. Image filter226 removes interference signals that may produce the same intermediatefrequency as the desired communication signal 195 after mixing thereceived signal 203 to an intermediate frequency in a superheterodynescheme. Thus, pre-selector filter 220 and image filter 226 generallyremove out-of-band interferers present in the received signal 203 whilepassing communication signal 195 and any in-band interferers present inthe received signal 203.

Pre-mixer 228 mixes the output of image filter 226 to translate thecommunication signal 195 to an intermediate frequency corresponding tothe center frequency of IF filter 230. In one embodiment, pre-mixer 228is implemented to up-convert the communication signal 195 to a higherintermediate frequency. Alternatively, pre-mixer 228 is implemented todown-convert the communication signal 195 to a lower intermediatefrequency. Thus the center frequency of IF filter 230 may be above orbelow the channel frequency of the communication signal 195. Localoscillator 234 is tuned to provide a signal frequency that is either thesum or the difference of the communication signal channel frequency andthe IF filter center frequency.

The pre-mixer 228 mixes the output of image filter 226 with the localoscillator signal to produce a signal that will include the originalcommunication signal channel frequency, the oscillator signal frequency,and the communication signal channel frequency translated to the IFfilter center frequency, as well as other unwanted signal frequenciesassociated with interferers.

For example, if the communication signal 195 is transmitted at a channelfrequency of 403 MHz and the IF filter 230 has a center frequency of 80MHz, the local oscillator 234 may be tuned to provide pre-mixer 228 a483 MHz signal or a 323 MHz signal. In a down-conversion operation,pre-mixer 228 will use a 483 MHz local oscillator signal to produce amixed signal having a component at the IF filter center frequency of 80MHz, equal to the difference of the local oscillator frequency 483 MHzand the communication signal channel frequency of 403 MHz.

In an alternative embodiment, local oscillator 234 is tuned to provide asignal to pre-mixer 228 that results in a mixed signal offset from thecenter frequency of the IF filter 230. This offset mixed signal is usedto increase interference rejection on one side of the desiredcommunication signal. The desired communication signal is offset towardan edge of the IF filter pass band, and interference signals occurringat frequencies adjacent to the desired communication signal undergo agreater offset from the IF filter center frequency, further into therejection portion of the IF filter. This offset mixing signal providedby the local oscillator 234 is desirable, for example, when interferencesignals occur with greater probability on one side of desiredcommunication signal frequency, i.e., either at higher frequencies or atlower frequencies than the desired communication signal.

Local oscillator 234 is tuned to provide the desired mixing frequency bya control signal received from loop filter 236 and synthesizer 238.Synthesizer 238 receives a control signal 242 and a reference clocksignal 244 from processor 210 for use in adjusting local oscillator 234.The control signal 242 communicates the frequency of a selectedcommunication channel when transceiver 208 is operating in a receivingmode. Synthesizer 238 locks the local oscillator frequency at anappropriate frequency for up- or down-conversion of the communicationsignal 195 to the IF filter center frequency. It is recognized that theexact local oscillator frequency used for translating the communicationsignal 195 to the IF filter center frequency will typically correspondto a multiple of the reference clock signal 244 provided by processor210.

The mixed signal output of pre-mixer 228 is filtered by IF filter 230.IF filter 230 has a pass band at least as wide as the communicationsignal channel bandwidth. IF filter 230 may represent a single filter ora series combination of filters selected to provide the desiredfrequency response, in particular a desired center frequency, pass bandwidth, and signal attenuation outside the pass band. The IF filter 230thus removes interferers outside this single channel bandwidth,including in-band interferers which fell within the transceivercommunication channel range prior to mixing by mixer 228.

In a superheterodyne receiver, an IF signal output of IF filter 230would typically be amplified and provided to a demodulator operating onthe IF frequency. In contrast, IRM 201 includes post-mixer 232 whichtranslates the IF filter output back to the original channel frequencyof the communication signal 195. Post-mixer 232 also receives input fromlocal oscillator 234 for essentially reversing the mixing operationperformed by pre-mixer 228. If pre-mixer 228 up-converts the receivedsignal 203, post-mixer 232 down-converts the IF filter output and viceversa. In this way, the output of post-mixer 232 includes thecommunication signal 195 translated back to its original channelfrequency, but both in-band and out-of-band interferers present in thereceived signal 203 will be removed or attenuated by IF filter 230.

In the example given above, received signal 203 includes communicationsignal 195 transmitted at a channel frequency of 403 MHz. Pre-mixer 228down-converts the 403 MHz signal to the IF filter center frequency of 80MHz using a local oscillator frequency signal of 483 MHz. Post-mixer 232will then up-convert the output of IF filter 230 having an IF of 80 MHzto the desired channel frequency of 403 MHz using the local oscillatorfrequency of 483 MHz.

The output of post-mixer 232 is provided to gain control 240. Gaincontrol 240 may be implemented as a variable gain amplifier receiving anautomatic level control signal 262 from processor 210. Gain control 240operates to maintain a uniform amplitude of the IRM output signal 270across the communication channel range of transceiver 208. Gain control240 provides consistent gain across varying frequencies and operatingtemperatures and compensates for amplitude variability, which may be anet gain or a net loss, of the cascaded components included in IRM 201.The IRM output signal 270 is thereby provided to transceiver 208 andincludes the communication signal 195 with a fixed gain (such as unitygain or other selected net gain or loss) and its original channelfrequency preserved. It is recognized that gain control 240 may beimplemented at other locations in the IRM 201 rather than after thepost-mixer 232. However, uniform gain of the communication signal 195across the channel range is expected to be optimally achieved byimplementing gain control 240 at the end of the cascade of IRM 201components.

Transceiver 208 receives IRM output signal 270 without requiring anyamplitude or frequency offset signals or any other adjustments ormodifications. In other words, the interference rejection processperformed by IRM 201 is transparent to transceiver 208. The IRM outputsignal 270 is provided to transceiver 208 with the original signalamplitude and frequency of the communication signal 195 substantiallypreserved, as if the communication signal 195 has been passed directlyfrom antenna 202 to transceiver 208 but with the major difference ofhaving both in-band and out-of-band interference signals removed orattenuated. Telemetry module 200 is thus more tolerant of interferenceallowing transceiver 208 to function as a high dynamic range receiverwithout altering or adjusting transceiver 208 itself. The IRM 201 can beconsidered a modular component in that it can be added “in front of” anexisting transceiver 208 in a telemetry module 200 without requiringdesign changes or modifications to the transceiver 208.

Control signal 242 from processor 210 allows local oscillator 234 to belocked into different frequencies corresponding to different channelsspanning an operating communication channel range. In this way, IRM 201can be adjusted to remove interferers from received signal 203 over arange of communication channels. Single channel frequencies over a rangeof operating channels can be scanned by telemetry module 200 through theadjustment of local oscillator 234 under control of processor 210. Avariable control signal 242 allows IRM 201 to pass communication signalscorresponding to the range of single channel frequencies spanning theoperating communication channel range. As transceiver 208 changeschannels, for example in response to a communication error, IRM 201 canimmediately be adjusted to pass communication signals corresponding tothe newly selected channel. Communication errors can occur in thepresence of co-channel interference signals. By moving to a differentchannel, those in-band interference signals falling in a previouslyselected channel bandwidth are attenuated by IRM 201.

Transceiver 208 receives the IRM output signal 270 and provides thereceived signal to processor 210. Processor 210 transfers received datato host interface 280 for use by the host medical device in whichtelemetry module 200 is incorporated. The received data may includeprogramming data used by the host device in controlling host devicefunctions or for transmission to another host device. The received datamay include an interrogation command instructing the host device toretrieve data from memory or in real-time for transmission by telemetrymodule 200 to the requesting medical device 190 or to a computernetwork.

FIG. 3 is a flow chart of one embodiment of a method for rejectinginterference during wireless telemetry communication. Flow chart 300 isintended to illustrate the functional operation of a telemetry module,and should not be construed as reflective of a specific form of softwareor hardware necessary to practice the illustrative method. It isbelieved that the particular form of hardware will be determinedprimarily by the particular system architecture employed in the deviceand by the particular telemetry methodologies employed by the device.Providing analog and/or digital hardware, software and/or firmware toaccomplish the described functionality in the context of any modernmedical device, given the disclosure herein, is within the abilities ofone of skill in the art.

Methods described in conjunction with flow charts presented herein maybe implemented, at least in part, in a computer-readable medium thatincludes instructions for causing a programmable processor to carry outthe methods described. A “computer-readable medium” includes but is notlimited to any volatile or non-volatile media, such as a RAM, ROM,CD-ROM, NVRAM, EEPROM, flash memory, and the like. The instructions maybe implemented as one or more software modules, which may be executed bythemselves or in combination with other software.

At block 302, a wireless telemetry signal is received by an antenna of atelemetry module. The wireless telemetry signal, also referred to hereinas the “communication signal”, undergoes pre-selection filtering atblock 304 and image filtering at block 306. Pre-selection filtering andimage filtering removes or attenuates out-of-band interferers asdescribed above in conjunction with FIG. 2.

At block 308, the filtered signal is translated or “mixed” to anintermediate frequency. The signal translation may involve up conversionor down conversion of the communication signal frequency to a higher orlower IF, respectively. At block 310, the translated signal is filteredusing an IF filter having a bandwidth at least as wide as the desiredcommunication channel bandwidth, but narrower than an operatingfrequency range including multiple channels. The filtered IF signal isthen translated or “mixed” back to the original communication channelfrequency at block 312.

Gain adjustment can be performed at block 316, e.g., using a variablegain amplifier and/or low noise amplifier, to provide an output signalhaving a fixed gain (such as unity gain or other selected net gain orloss) relative to the received communication signal. The gain adjustmentmaintains the amplitude of the output signal at the expectedcommunication channel amplitude. In this way, an output signal providedto a receiver at block 320 is characterized by a frequency and amplitudeapproximately equal to the intended communication signal frequency andamplitude but both in-band and out-of-band interferers are been removedor attenuated.

FIG. 4 is a plot of the insertion loss 350 of an IF filter appropriatefor use in IRM 201 of FIG. 2. The illustrative IF filter ischaracterized by a center frequency 352 of 170.6 MHz and pass band 354of approximately 170.45 MHz to 170.75 MHz, corresponding to a singlecommunication channel bandwidth of 300 KHz. Limited amplitudeattenuation and ripple of less than 1 dB within this pass band 354minimizes the impact of the IF filter on the amplitude of a receivedcommunication signal translated to the IF filter center frequency 352.Interferers falling outside this pass band 354, however, will besignificantly attenuated.

FIGS. 5A through 5E are plots of the output signal of an IRM for fivedifferent RF communication channel frequencies. An IRM was implementedaccording to the IRM 201 shown in FIG. 2 using a 170.6 MHz IF filter. InFIG. 5A, a wireless telemetry signal at 401.05 MHz is received and mixedusing a local oscillator frequency of 571.65 MHz (equal to the sum ofthe 401.05 MHz channel frequency and 170.6 MHz IF filter centerfrequency). In this example, the telemetry signal is firstdown-converted to the intermediate frequency by the pre-mixer thenup-converted back to the communication signal channel frequency by thepost-mixer. As can be seen in FIG. 5A, the output signal 402 of the IRMmodule has minimal insertion loss along the channel bandwidth 403 withsignificant out-of-band interference rejection.

Analogous IRM output signals 404 through 410 can be seen in FIGS. 5Bthrough 5E, respectively, for other channel frequencies corresponding toeach of: 402.15 MHz (output signal 404 in FIG. 5B) mixed using a localoscillator frequency of 572.75 MHZ; 403.35 MHz (output signal 406 inFIG. 5C) mixed using a local oscillator frequency of 573.95 MHz; 404.85MHz (output signal 408 in FIG. 5D) mixed using a local oscillatorfrequency of 575.45 MHz; and 405.95 MHz (output signal 410 in FIG. 5E)mixed using a local oscillator frequency of 576.55 MHz. The illustratedchannel frequencies represented by the output signals 402 through 410 inFIGS. 5A through 5E correspond to channels defined by the MEDs and MICsbands.

FIG. 6 is a functional block diagram of a telemetry module 500 includingan IRM 501. Telemetry module 500 includes an antenna 502, IRM 501,pre-IRM switch 504, post-IRM switch 506, processor 510 and transceiver508. Antenna 502 is provided for receiving off-the-air radio frequency(RF) signals transmitted by another medical device 490 and fortransmitting communication signals from transceiver 508. Processor 510controls transceiver 508 to operate in either a transmission mode or ina receiving mode. During a transmission mode, processor 510 provides acontrol signal 560 to pre- and post-IRM switches 504 and 506 to select atransmission pathway from an RF antenna port 550 to antenna 502 viaswitches 504 and 506 bypassing IRM 501. During a receiving mode,processor 510 provides a control signal 560 to pre- and post-IRMswitches 504 and 506 to select a receiving pathway from antenna 502through IRM module 501 to transceiver 508.

During a receiving mode, antenna 502 receives a signal 503 whichincludes a desired communication signal 495 transmitted by anotherdevice 490 and can include various interference signals. The desiredcommunication signal 495 is a wireless telemetry signal transmitted frommedical device 490 at a selected channel frequency having a relativelynarrow bandwidth. The received signal 503 may include both in-band andout-of-band interferers as generally described above in conjunction withFIG. 2.

IRM 500 includes pre-selector filter 520, low noise amplifier 522,pre-selection switch 524, post-selection switch 526, filter bank 530,and gain control 540. Pre-selector filter 520 is a bandpass filter whichpasses signal frequencies corresponding to a range of operating channelsover which transceiver 508 is configured to communicate. As previouslydescribed, in one embodiment pre-selector filter 520 passes frequenciesin the range of 401 MHz to 406 MHz corresponding to the MEDS and MICSchannel frequencies often used in implantable medical device telemetrysystems. As such, pre-selector filter 520 attenuates out-of bandsignals. Low noise amplifier 522 reduces the insertion loss ofcommunication signal 495.

Pre-selection switch 524 and post-selection switch 526 are multi-poleswitches used to select a filtering pathway through filter bank 530corresponding to the frequency of the communication signal 495. Filterbank 530 includes two or more channel-specific filters 532 through 538which are selectable using pre-selection and post-selection switches 524and 526. Switches 524 and 526 are controlled by a control signal 542provided by processor 510. Control signal 542 corresponds to the channelfrequency of the communication signal 495.

Each channel-specific filter 532 through 538 included in filter bank 530is implemented to have a center frequency corresponding to at least onecommunication channel frequency. Each filter 532 through 538 is furthercharacterized by a pass band that is at least as wide as a singlechannel bandwidth but narrower than the overall channel range. Forexample, in one embodiment filters 532 through 538 are each provided asRF filters having a center frequency corresponding to at least onechannel frequency included in the selected channel range of 401 to 406MHz and each having a pass band of approximately 1.25 MHz.

Each of filters 532 through 538 may be embodied as a single filter or aseries combination of filters to achieve the desired frequency response,i.e., a desired center frequency, pass band width, and signalattenuation outside the pass band. Furthermore, filters 532 through 538may be selectable one at a time or in series combinations using switches(not shown) implemented within filter bank 530. In other words, filterbank 530 may be implemented as a network of switchable filters allowingdifferent series combinations or single filters to be selected accordingto a selected operating channel.

The filtering provided by each channel-specific filter 532 through 538removes interferers within the communication channel range by parsingthe operating bandwidth of the overall communication channel range oftransceiver 508 into segments containing one or more of the specificchannels utilized in the channel range. It is recognized that a singlefilter within filter bank 530 may have a pass band that overlaps morethan one channel frequency. As such, a single filter within filter bank530 may be selected by multi-pole switches 524 and 526 for more than onecommunication signal frequency. Through implementation of customdesigned filters, single channel selectivity may be realized orapproximated. In one embodiment, each filter 532 through 538 included inbank 530 has a center frequency and pass band encompassing at least onesingle channel frequency and bandwidth. Each filter may encompass adifferent number of channels that other filters within filter bank 530.Single channel frequencies over a range of communication channels overwhich transceiver 508 operates can be scanned by telemetry module 500through the control of multi-pole switches 532 through 538 under thecontrol of processor 510. It is recognized that the number of filtersimplemented in bank 530 will depend on the number of channels whichtransceiver 508 operates on and the channel resolution achieved by theimplemented filters. In telemetry systems utilizing ultrasound, infraredor other frequency bands, the filters used to form filter bank 530 maybe selected accordingly.

The output of filter bank 530 is passed to gain control 540 viapost-selection switch 526. Gain control 540 may be implemented as avariable gain amplifier receiving a control signal 562 from processor510. As described previously, gain control 514 maintains a uniform gainoutput signal 570 across the communication channel range. Output signal570 has a frequency equal to the desired communication signal 495, butwith both in-band and out-of-band interferers removed or attenuated bypre-select filter 520 and filter bank 530.

The output signal 570 of IRM 501 is provided to transceiver 508 withoutadjustment or modification of transceiver 508. As such, IRM 501 operatestransparently to transceiver 508. Telemetry module 500 is thus providedwith an increased dynamic range without requiring a redesign ormodification of transceiver 530.

Transceiver 508 receives the IRM output signal 570 and provides receiveddata to processor 510. Processor 510 transfers received data to hostinterface 580 for use by the host medical device in which telemetrymodule 500 is incorporated. The received data may include programmingdata used by the host device in controlling host device functions. Thereceived data may include an interrogation command instructing the hostdevice to retrieve data from memory or in real-time for transmission bytelemetry module 500 to the requesting medical device 490.

FIG. 7 is a flow chart of one embodiment for rejecting interference in amedical device telemetry module. In method 600, a wireless telemetrysignal is received at block 602 by an antenna of a telemetry module. Thewireless telemetry signal, also referred to herein as the “communicationsignal”, undergoes pre-selection filtering at block 604 to remove orattenuate out-of-band interferers.

At block 606, a channel-specific filter is selected according to thecurrent operating channel frequency. The received signal is filtered bya channel-specific filter at block 608. The channel specific filter hasa center frequency corresponding to the selected communication channeland a pass band narrower than the overall communication channel rangeover which an associated transceiver operates. Channel specificfiltering at block 608 thus removes in-band interferers.

Gain adjustment can be performed at block 610, e.g., using a variablegain amplifier and/or low noise amplifier, to reduce insertion loss andthereby provide an output signal having a fixed gain (such as unity gainor other selected net gain or loss) relative to the desiredcommunication signal across channel frequencies and operatingtemperatures. In this way, an output signal provided to a receiver atblock 612 is characterized by a frequency approximately equal to thedesired communication signal frequency, but both in-band and out-of-bandinterferers have been removed or attenuated.

Thus, a telemetry module and interference rejection methods have beenpresented in the foregoing description with reference to specificembodiments. It is appreciated that various modifications to thereferenced embodiments may be made without departing from the scope ofthe invention as set forth in the following claims.

1. A wireless telemetry module, comprising: an antenna configured toreceive a communication signal having a channel frequency and having achannel bandwidth; a transceiver configured to operate over a channelrange of single channel frequencies including the channel frequency; aprocessor coupled to the transceiver and configured to control thetransceiver to operate in a receiving mode and in a transmitting mode;an interference rejection module configured to receive control signalsfrom the processor, the interference rejection module coupled betweenthe antenna and the transceiver when the transceiver is operating in thereceiving mode, the interference rejection module attenuatinginterference signals occurring in the received signal and falling withinthe channel range and outside the channel range in response to theprocessor control signals, the interference rejection module providingthe transceiver with the communication signal at the channel frequency.2. The wireless telemetry module of claim 1 further comprising: a firstswitch coupled between the antenna and the interference rejectionmodule; and a second switch coupled between the interference rejectionmodule and the transceiver, the first and second switches configured toreceive a control signal from the processor to cause the first andsecond switches to switch between a first state coupling theinterference rejection module between the antenna and the transceiverduring the transceiver receiving mode and a second state bypassing theinterference rejection module during the transceiver transmitting mode.3. The wireless telemetry module of claim 2, wherein the transceiver isconfigured to receive a range of single channel frequencies and whereinthe interference rejection module comprises: a first filter configuredto attenuate interference signals occurring in the received signalfalling outside of the channel range; and a second filter configured toattenuate interference signals occurring in the received signal fallingwithin the channel range.
 4. The wireless telemetry module of claim 3,wherein the second filter comprises a intermediate frequency filter andthe interference rejection module further comprises: a first mixer forreceiving the received signal; an intermediate frequency filterincluding a center frequency and a pass band; a second mixer; and alocal oscillator configured to provide a mixing signal; wherein, thefirst mixer is configured to translate the communication signal to fallwithin the intermediate frequency filter pass band in a mixed signaloutput, the intermediate frequency filter is configured to filter themixed signal output, and the second mixer is configured to receive thefiltered mixed signal output and the local oscillator signal andtranslate the filtered mixed signal back to the channel frequency,wherein the local oscillator receives a control signal from theprocessor for controlling the local oscillator mixing signal frequency.5. The wireless telemetry module of claim 4 wherein the first mixer isconfigured to translate the communication signal to the intermediatefrequency, based up the local oscillator mixing signal frequency iscontrolled to cause filter center frequency.
 6. The wireless telemetrymodule of claim 4 wherein the local oscillator mixing signal frequencyis controlled to cause the first mixer to translate the communicationsignal to an intermediate frequency filter pass band frequency offsetfrom the center frequency.
 7. The wireless telemetry module of claim 4wherein the processor is configured to provide the local oscillator witha variable control signal to cause the interference rejection module topass communication signals to the transceiver corresponding to the rangeof single channel frequencies.
 8. The wireless telemetry module of claim4 wherein the intermediate frequency filter comprises a seriescombination of filters.
 9. The wireless telemetry module of claim 3further comprising: a first multi-pole switch and a second multi-poleswitch, wherein the second filter comprises a plurality of selectablechannel-specific filters each having a center frequency corresponding toat least one single channel frequency and the first multi-pole switchand the second multi-pole switch receiving a control signal from theprocessor for selecting a channel-specific filter corresponding to thechannel frequency.
 10. The wireless telemetry module of claim 9 whereineach of the plurality of selectable channel-specific filters having apass band less than the channel range.
 11. The wireless telemetry moduleof claim 9 wherein one of the plurality of selectable channel-specificfilters comprises a series combination of filters.
 12. The wirelesstelemetry module of claim 9 wherein the plurality of selectablechannel-specific filters are selectable in series.
 13. The wirelesstelemetry module of claim 1 further comprising a diplexer for frequencyduplexing the received signal with a simultaneously transmitted signalbeing transmitted by the transceiver.
 14. A method, comprising:receiving a wireless signal comprising a communication signaltransmitted at a channel frequency and having a single channelbandwidth; controlling a transceiver to operate in a receiving mode andin a transmitting mode over a channel range of single channelfrequencies including the channel frequency; coupling an interferencerejection module between an antenna receiving the wireless signal andthe transceiver when the transceiver is operating in the receiving mode;controlling the interference rejection module to attenuate interferencesignals occurring in the received signal and falling outside the channelbandwidth within the channel range and outside the channel range inresponse to the processor control signals; and providing the transceiverwith the communication signal at the channel frequency.
 15. The methodof claim 14, further comprising providing a control signal to a firstswitch coupled between the antenna and the interference rejection moduleand to a second switch coupled between the interference rejection moduleand the transceiver to cause the first and second switches to switchbetween a first state coupling the interference rejection module betweenthe antenna and the transceiver during the transceiver receiving modeand a second state bypassing the interference rejection module duringthe transceiver transmitting mode.
 16. The method of claim 15, whereinthe transceiver is configured to receive a range of single channelfrequencies and wherein attenuating the interference signals comprises:filtering the received signal using a first filter having a pass bandcorresponding to the channel range; and filtering the received signalusing a second filter having a pass band narrower than the channelrange.
 17. The method of claim 16, wherein the second filter comprises aintermediate frequency filter having a pass band and a center frequencyand the method further comprises: generating a local oscillator signalcorresponding to one of a sum and a difference of the channel frequencyand a frequency within the intermediate frequency filter pass band;mixing the received signal and a local oscillator signal for translatingthe communication signal to fall within the intermediate frequencyfilter pass band in a mixed signal output, filtering the mixed signaloutput using the intermediate frequency filter, and mixing the filteredmixed signal output and the local oscillator signal for translating thefiltered mixed signal back to the channel frequency.
 18. The method ofclaim 17 wherein the local oscillator signal corresponds to one of a sumand a difference of the channel frequency and the intermediate frequencyfilter center frequency.
 19. The method of claim 17 wherein the localoscillator signal corresponds to one of a sum and a difference of thechannel frequency and an intermediate frequency filter pass bandfrequency offset from the center frequency.
 20. The method of claim 17wherein the local oscillator signal is a variable control signalcorresponding to the channel range.
 21. The method of claim 17 whereinthe intermediate frequency filter comprises a series combination offilters.
 22. The method of claim 14 wherein the second filter comprisesa plurality of selectable channel-specific filters each having a centerfrequency corresponding to at least one single channel frequency, themethod further comprising selecting a channel-specific filtercorresponding to the channel frequency.
 23. The method of claim 22wherein each of the plurality of selectable channel-specific filtershaving a pass band less than the channel range.
 24. The method of claim22 wherein one of the plurality of selectable channel-specific filterscomprises a series combination of filters.
 25. The method of claim 22wherein selecting a channel-specific filter comprises selecting at leasttwo of the plurality of selectable channel-specific filters in series.26. The method of claim 14 further comprising a frequency duplexing thereceived signal and a simultaneously transmitted signal.
 27. A medicaldevice system, comprising; a first medical device comprising a firsttelemetry module transmitting a wireless communication signal at achannel frequency having a channel bandwidth; and a second medicaldevice comprising a second telemetry module adapted for bidirectionalcommunication with the first telemetry module over a channel range ofsingle channel frequencies; the first telemetry module comprising anantenna configured to receive a communication signal transmitted at achannel frequency and having a channel bandwidth; a transceiver; aprocessor coupled to the transceiver and controlling the transceiver tooperate in a receiving mode and in a transmitting mode; an interferencerejection module configured to receive control signals from theprocessor, the interference rejection module coupled between the antennaand the transceiver when the transceiver is operating in the receivingmode, the interference rejection module attenuating interference signalsoccurring in the received signal and falling outside the channelbandwidth within the channel range and outside the channel range inresponse to the processor control signals, the interference rejectionmodule providing the transceiver with the communication signal at thechannel frequency.